We have found that quiescent hamster sperm from the cauda epididymis contain low levels of cAMP and that their motility is activated during the initiation of cAMP synthesis. This event is apparently triggered by contact with prostatic calcium ion. We have also observed that external cyclic nucleotides can by-pass this requirement for calcium but that due to the presence of a previously undetected cyclic nucleotide phosphodiesterase in epididymal fluid, this does not occur in vivo. In addition we have found that motile sperm do not exhibit their usual sensitivity to dilution if a molecule from epididymal fluid is present in the diluent. The proposed research is designed to answer several major questions raised by this and more recent data and, where possible, to apply the answers both to male contraception and to the storage of viable spermatozoa. BIBLIOGRAPHIC REFERENCES: Rayner, M., Sanders, B., Harris, S., Lin, Y.C., and Morton, B. Palytoxin: Effects on Contractility and 45Ca ion Uptake in Isolated Ventricular Strips. Res. Comm. Chem. Path. Pharm. 11, 55 (1975). Chang, T.S.K. and Morton, B. Epididymal Sulfhydryl Oxidase: Sperm-Protective Enzyme From the Male Reproductive Tract. Biochem. Biophys. Res. Comm. 66, 309-315 (1975).